Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$169.53	12.674%	$191.0162	$191.02	$191.00	$191.00
Purchase #2	$139.81	8.474%	$151.6575	$151.66	$151.65	$151.70
Purchase #3	$123.86	13.469%	$140.5427	$140.54	$140.55	$140.50
Purchase #4	$204.26	9.392%	$223.4441	$223.44	$223.45	$223.40
Purchase #5	$25.30	12.718%	$28.5177	$28.52	$28.50	$28.50
Purchase #6	$41.33	3.674%	$42.8485	$42.85	$42.85	$42.80
Purchase #7	$66.62	7.395%	$71.5465	$71.55	$71.55	$71.50
7 purchase totals =	$770.71		$849.5732	$849.58	$849.55	$849.40